The work supported by this project is part of an ongoing effort to clarify the relative roles, if any, of thymus-derived lymphocytes (T cells), bone marrow-derived lymphocytes (B cells), and macrophages in resistance to infection by intracellular bacteria. The model system used involves injection of mice with the intracellular bacterium Listeria monocytogenes. During the coming year, we will be comparing biologic activities of two materials isolated from Listeria: a purified cell wall fraction (PF), and an intracellular product (LIP) which, unlike PF, is probably a protein. The ability of these materials to be B cell mitogens, adjuvants, and polyclonal activators will be studied. In addition their effects on macrophage function and in the ability of mice to resist infection will be explored. Another area of emphasis will be on the biologic activities of anti-Listeria antibodies, with an emphasis on their possible function as opsonins.